1. Field of the Invention
The present invention relates to a turret punch press, and, in particular, to a turret punch press on which is mounted a plurality of turrets.
2. Description of the Prior Art
As is commonly known, a conventional turret punch press comprises: a C-shaped frame integrally provided with an upper frame and a lower frame; a workpiece transfer and positioning device supported in a freely transferable manner in the X-axis and Y-axis directions on the frame, a plate-shaped workpiece which is to be transferred and positioned in the X-axis and Y-axis direction; a plurality of freely rotatable upper turrets, each of which supports a plurality of punches for punching the workpiece; a plurality of lower turrets, each of which supports a plurality of dies in opposition to the above-mentioned punches; and a striker provided with free vertical motion on the frame for striking the punches.
In a turret punch press with such a configuration the number of punches and dies which can be mounted at one time on the upper and lower turrets is limited, which imposes limitations on the processing.
Accordingly, in recent years, in order to increase the variety of processing, technology has been developed for automatically mounting/dismounting and changing the punches and dies on the upper and lower turrets, using an automatic tool changing device, for example, as disclosed in U.S. Pat. No. 4,624,044 and in Japanese Laid open Patent Application No. 63-26225.
However, in this conventional technology, the problem arises that, when the punches and dies are changed on the upper and lower turrets of the turret punch press, the punching operation on the plate-shaped workpiece must be halted, to the detriment of the operating efficiency.